How to build Long Distance Reception Rhombic Tv Antennas. The 1951 article has easy to follow directions. At the http://www.wtfda.org/ web site , in the search box at the wtfda web site , type in the word , rhombic . or for more articles on Tv antennas , type in the word , antennas.

Last edited by mtownsend; 9-Apr-2012 at 10:14 PM.
Reason: Restored original post

Here is some additional information, including a link to "Edmund Laport's textbook Radio Antenna Engineering, published in 1952 and now out of copyright and freely available, scanned and processed into PDF by Dave Platt, AE6EO." (This is a 25 MB file)

Rhombic? What's that? Obviously, this is a forum for antenna gurus who understand the lingo. It sounds like reinventing the wheel, making a homemade antenna. Heck, I don't even bake from scratch, preferring the easy route of box mixes.

Speaking of which, I wonder if the antenna advertised on this page for "150 mile range" is any good or worth the money. I do know that the prices have been dropping since I bought mine at the beginning of the switch in 2/2008. You can get a Winegard SquareShooter for about $70 bucks these days and I'm sure the rotors prices are falling too.

I just bought mine from a reputable company (Winegard) online. The only thing I wonder is if I could be picking-up even more channels even further away. Mine was advertised to pick-up signals within a 50 mile radius but it goes much further out.

I can't help but wonder if those who wander in here can really be helped. That is, people who know nothing about radio/tv frequencies and how they work. I'm sure most don't wish to read a book to figure this thing out. I know that I wouldn't. It would merely discourage me further.

Notice that "Enthusiast's Exchange" is at the bottom of the list of forums.

Enthusiast's Exchange could be code for 'the place for kids with pocket protectors and those who wish they were'.

Yes I have a hobby interest in building antennas.

As far as 'fantastic miracle antennas' are concerned, if it sounds too good to be true, it probably isn't true.

As far as helping people goes, at least a few have made the effort to post back after using the advise offered... reporting success. I hope many others are just to busy watching TV to post back their results.

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If the well is dry and you don't see rain on the horizon, you'll need to dig the hole deeper. (If the antenna can't get the job done, an amp won't fix it.)

The only thing I wonder is if I could be picking-up even more channels even further away. Mine was advertised to pick-up signals within a 50 mile radius but it goes much further out.

I can't help but wonder if those who wander in here can really be helped. That is, people who know nothing about radio/tv frequencies and how they work. I'm sure most don't wish to read a book to figure this thing out. I know that I wouldn't. It would merely discourage me further.

Have you tried using TVFool? Prior to having this resource, the average consumer had to rely on friends and the claims of manufacturers. With this site, you can determine the requirements the antenna must meet with reasonable precision. You can then use performance documentation posted by the better manufacturers to determine the best fit yourself, or you can show your report to a group who are eager to help. If you have browsed the "help with reception" forum, then you shouldn't have to wonder about getting help.

I encourage you to try this out. One key to best results is using an accurate receive location, so I suggest using this method. After entering your details, you'll get back a page with an receive location icon on a Google map. Ensure that the icon is in the right place by zooming in and dragging the icon as needed. Adjust the antenna height as needed, then click the "make radar plot button."

The report you get back (it's bookmarkable) has information presented in different formats. There is a very helpful signal analysis FAQ that's linked to at the top of your report. You should read that before doing anything else. If you need further help, post your question, along with the URL of your report, in the "help with reception" forum.

27 dBd WOW How good is that projection? I have got to build one of these! (maybe scaled a little more toward ch 30) Are there any plots or has anyone modeled this? If not can anyone project what the gain is at way off frequency? For example :scaling the antenna to 630 mhz ~ch 40 would make the each of the 4 elements ~178" long which is the wave length of VHF ch 4. Any idea what kind of gain (if any) this gets at ch 4 frequency?

The older documentation on rhombic antennas often comments on the low SWR over a fairly wide frequency range (2:1 is referred to as I recall), that is not an indication constant forward gain though. The rhombic is a non-resonant antenna, an optimized long-wire design. It's relatively constant input impedance over a wide range of frequencies is the result of it's traveling wave design with resistive termination. The goal of the design is to align the lobes of the individual legs to work together in one direction. The lobes of radiation from a long wire antenna are frequency dependent so it would be logical to assume that as you move away from the design frequency, the forward gain will become 'un-focused'. With good modeling software, exploring the effects of off frequency operation is far easier than it was in the late 40's and early 50's when Laport was number crunching on slide-rule and note pad.

The same shape can be scaled to operate on VHF channel 4 and would have the same gain. The antenna would be about 10 times larger.

Cut for channel 30, the short element would be 71.875" and the long element would be 123.214" which results in the front to rear length a bit more than 181" and the width about 80".

(I have a specific interest in UHF-46...)

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If the well is dry and you don't see rain on the horizon, you'll need to dig the hole deeper. (If the antenna can't get the job done, an amp won't fix it.)

I looked at the ca forum and none of the posted models were quite like the pdf.
So I tried my hand at modeling it, I came up with 15.4 dBi @ 585 MHz.
Pretty good but not phenomenal (like 27 dBi) so I won't be building one.
And my quest for a 20+ dBi DX antenna continues.

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the same shape can be scaled to operate on VHF channel 4 and would have the same gain. The antenna would be about 10 times larger.

Thanks but not an option for my location ,it would hang over the property lines.
BTW. I did run the model (not scaled) at 69 MHz. and got 3.4 dBi at 90 and 270 deg. accounting for a SWR of 9.7 means a dipole is much better.
If I still lived on 14 acres in the country I'd pound in some 6'6 fence posts and use electric fence wire and insulators and play with it. But for now I'll abandon this design and continue the quest.
Best I've found is 18.5 dBi any suggestions (no VHF needed as I'll build a custom cut yagi for ch. 4)

Some of the older information I've come across includes descriptions of a dual stack in which the upper and lower sections are tied together with a piece of open wire or twin lead and the transmission line is connected to the lower rhombic section feed point. This results in imbalanced current and voltage in the upper and lower sections and also drives the upper section out of phase with the lower section at any frequency other than one resulting in the phasing tie being 1/2 wave in electrical length (Or an odd multiple of a half wave. But three or five times the design frequency puts you in microwave ranges.) The vertical beam then skews up or down as the frequency moves away from design center.

So, I simply used a balanced feed arrangement which is not my invention. As you say, the technique has been used in most panel antenna designs. Notice in the quad stack, the top and bottom phasing lines are twisted 180° (a phase reversal at the design frequency), the center phasing link has no phase reversal.

Over real ground, I'd expect to see the pattern launch upward at anywhere from 2 to 12 degrees... depending on the antenna height and ground characteristics.

I have no plan to rotate this with a CM-9521a

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If the well is dry and you don't see rain on the horizon, you'll need to dig the hole deeper. (If the antenna can't get the job done, an amp won't fix it.)

Why in the world would anyone go to all of the trouble to build any antenna when you can buy an antenna on line for $58.00 that will receive stations 150 miles away? This must have a gain of 30 db! HA! HA! HA! So anyone that is focused on antenna gain or chooses an antenna based on the manufactures claims of distance, listen up.
The world is not flat! All UHF signals fall into the "sky wave" catagory. This sets up a "radio horizon" about 80 miles out. On a clear site void of interferrence any good antenna with a gain around 9 dbi. will receive these stations.

The answer varies from one Enthusiast to another... This is the Enthusiast Exchange forum after all.

Some may have the misguided notion that they could save money (but I've built several from scrap bin material for a total of $0 out of pocket. Two of which are in service, reliably receiving several difficult edge path or distant signals.)

There are DXing hobbyists... For them, variable propagation is an opportunity to enjoy the 'hunt'.

Another reason is that a custom pattern may be needed due to adjacent and co-channel interference. Also, stations may be scattered around the compass.

Yet another, not everyone has a clear LOS, the need for more than 9dBi gain is common.

I'm sure there are other valid reasons... However, over in the Help with Reception forum, you'll not find a lot of 'roll your own' being suggested, certainly not as a 'first / best' solution.

Your point regarding fixation on any one parameter is valid. Thinking that gain is good without understanding the other factors that affect reception often leads people to buy amplifiers and sometimes antennas that make their situation worse, not better.

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If the well is dry and you don't see rain on the horizon, you'll need to dig the hole deeper. (If the antenna can't get the job done, an amp won't fix it.)

First let me say it would have to be a very special post to incite me to suggest this antenna.

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Originally Posted by signals unlimited

Why in the world would anyone go to all of the trouble to build any antenna

Why in the world would anyone buy an antenna when they can build their own?

Quote:

So anyone that is focused on antenna gain or chooses an antenna based on the manufactures claims of distance, listen up.

All the enthusiasts here I'm sure know distance claims are a joke and not to be trusted.
Besides SWR what other performance specs do you think we should consider more than gain? Not amplifier gain but antenna directivity gain.

Quote:

The world is not flat! All UHF signals fall into the "sky wave" catagory. This sets up a "radio horizon" about 80 miles out. On a clear site void of interferrence any good antenna with a gain around 9 dbi. will receive these stations.

9 dBi really? That only holds true if you live walking distance to walgreens world where they sell spherical chickens in vacuum packed canisters.
Cause where my antenna is is far from clear and there is nothing I can do to improve the site so I improve the antenna.
Personally I don't think there is an antenna with less than 12 dBi that can reliably receive a station I have 3 miles away. (Multipath nightmare) Higher gain is more undesirable signal rejection.
If I had the space I'd build one of these in a heart beat just to play.